This invention relates to an improved clamp utilizing improved inserts for clamping and holding drilling tubulars such as drill pipe. The clamp and inserts of this invention are particularly useful in connection with makeup and breakout wrenches used with drilling rigs for drilling bore holes in earth formations.
During drilling operations it is necessary to screw together threaded lengths of drilling tubulars such as drill pipe and casing. For example, with drill pipe, the threaded joints between adjacent lengths of drill pipe must be tightened to a specified torque (made up) and then later unscrewed from one another (broken out) during the drilling process. It is known to the art to provide makeup and breakout wrenches in drill rigs particularly for the purpose of applying the necessary torques needed to assemble and disassemble a drill string. U.S. patent application Ser. No. 269,279, filed June 1, 1981 and assigned to the assignee of the present invention, discloses one set of such makeup/ breakout wrenches.
Though prior art makeup/breakout wrenches have worked efficiently in many applications, there is a need for an improved wrench capable of exerting higher torques on drilling tubulars, without allowing the tubulars to slip with respect to the wrenches. The problem of slippage between the tubular and the makeup/breakout wrenches is particularly acute in connection with small diameter drilling tubulars, where extremely high levels of friction between the jaws of the makeup/breakout wrenches and the drilling tubulars may be required.